Optical Measurements, Morphology, and the Faraday Eﬀect Xunshan Liu, Emigdio E

www.acsami.org Research Article

Finely Designed P3HT-Based Fully Conjugated Graft Polymer: Optical Measurements, Morphology, and the Faraday Eﬀect Xunshan Liu, Emigdio E. Turner, Valerii Sharapov, Dafei Yuan, Mohammad A. Awais, Jeﬀrey J. Rack,* and Luping Yu*

Cite This: ACS Appl. Mater. Interfaces 2020, 12, 30856−30861 Read Online

ACCESS Metrics & More Article Recommendations *sı Supporting Information

ABSTRACT: In this work, our group synthesized and characterized a fully conjugated graft polymer comprising of a donor− acceptor molecular backbone and regioregular poly(3-hexylthiophene) (RRP3HT) side chains. Here, our macromonomer (MM) was synthesized via Kumada catalyst transfer polycondensation reaction based on ditin-benzodithiophene (BDT) initiator. The tin content of MM was then investigated by inductively coupled plasma-mass spectrometry (ICP-MS), which allowed for accurate control of donor/acceptor monomer ratio of 1:1 for the following Stille coupling polymerization toward our graft polymer (BP). The structures of the polymers were then characterized by gel permeation chromatography (GPC), NMR, and elemental analysis. This was followed by the characterization of optical, electrochemical, and physical properties. The magneto-optical activity of graft polymer BP was then measured. It was found that, despite the presence of the acceptor backbone, the characteristic large Faraday rotation of RRP3HT was maintained in polymer BP, which exhibited a Verdet constant of 2.39 ± 0.57 (104) °/T·m. KEYWORDS: synthesis, conjugated grafting polymer, grafting through, P3HT, Faraday eﬀect

1. INTRODUCTION molecular backbone may be not active enough to initiate the growth of the side chains because of the electrical properties of Architectural design and control of polymer structures is a 11 continuously pursued research effort. One is looking for new the backbone. Second, the side chains may grow randomly and thus causing differences in the degree of polymerization properties from different structures because the function could (DP). Third, it is almost impossible to ensure that all of the also follow form. Recent years have witnessed a rapid active sites along the molecular backbone are fully reacted, and development of numerous organic semiconducting polymers 1−3 thus generating structural defects. For the grafting through for applications in a wide range of areas. Among these, − method, a macromonomer with two functional groups is Downloaded via UNIV OF NEW MEXICO on August 31, 2020 at 02:33:20 (UTC). donor acceptor copolymers have been extensively inves- prepared for copolymerization. However, since the macro- tigated. While the majority of efforts have been devoted monomer’s molecular weight is not fixed (different lengths for toward developing new building blocks for these polymers,

See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. side chains), one can only roughly estimate the number of the developing novel chemistry to synthesize new architectures of functional groups by NMR or gel permeation chromatography conjugated polymers has been seldom reported. For instance, (GPC) and hence making it impossible to control a 1:1 ratio developing fully conjugated graft copolymers comprising of for the two monomers leading to a low degree of polymer- different types of polymers in the backbone and side chains has 4 ization. Another key reason of limited developments in this been rarely reported.4,5 The ability to combine two kinds of field might be the lack of related applications. The reported polymers with different properties in a single graft polymeric graft polymers did not show promising properties for their system offers potentials not available in each individual 6−8 potential application. For example, the authors tried to apply material. these materials to organic field-effect transistors; however, the To the best of our knowledge, there are only two papers to obtained charge mobilities were too low for good device have studied conjugated graft polymers that may be because of some inherent limitations of these two methods. Kumada catalyst transfer polycondensation (KCTP) has been widely Received: May 4, 2020 − used for synthesizing graft polymers.9 11 Previous studies have Accepted: June 15, 2020 already demonstrated both “grafting from” and “grafting Published: June 15, 2020 through” methods for synthesizing fully conjugated graft polymers employing KCTP polymerization.4,5 As for the grafting from method, the functionalized reactive sites on the

© 2020 American Chemical Society https://dx.doi.org/10.1021/acsami.0c08170 30856 ACS Appl. Mater. Interfaces 2020, 12, 30856−30861 ACS Applied Materials & Interfaces www.acsami.org Research Article performance. Therefore, a well-designed method to synthesize ratio of MM to the other monomer for the Stille polymers with high DP, less traps, and fixed side chain length is polycondensation. The structures of the resulting brush needed; appropriate applications for this kind of materials are polymers were investigated, and their thermal, photophysical, demanded. and electrochemical properties were studied. More impor- In this work, we developed a new method for synthesizing tantly, a new application, Faraday rotation, induced by polymer fully conjugated graft polymers (BP), as shown in Figure 1.A BP was investigated. It was found that the regioregular P3HT side chains in polymer BP maintained the large magneto- optical activity previously demonstrated for pure RRP3HT. The specific packing morphology of RRP3HT that yields large magneto-optical activity is still a subject of on-going − study.12 15 Furthermore, the effect of an acceptor domain on the thin-film “giant Faraday rotation” has previously not been studied. The maintained Faraday rotation implies that the packing of RRP3HT side chains forms extended domains, which exhibit properties similar to pure RRP3HT. Figure 1. Synthetic routes for the brush polymer. 2. RESULTS AND DISCUSSION 2.1. Synthesis and Characterization. The polymer ditin-benzodithiophene (BDT) unit with two chlorothio- structure and synthetic route are shown in Scheme 1. The phenes as pendant groups was functionalized with two structures of the monomers and copolymers were confirmed trimethyltin groups. Then, regioregular P3HT (RRP3HT) by 1H NMR, matrix-assisted laser desorption ionization time- chains were grown from the chlorothiophene unit by the of-flight (MALDI-TOF), and elemental analysis. The two KCTP method to yield a macromonomer (MM) showing a polymers exhibited excellent solubility in common organic low polydispersity index (Đ) of 1.25. The trimethyltin groups solvents such as chloroform, tetrahydrofuran (THF), and survived the Kumada condition, and the tin content of MM chlorobenzene. Table 1 summarizes the polymerization results was investigated with inductively coupled plasma-mass and thermal properties of the copolymers. The molecular Đ spectrometry (ICP-MS) allowing us to accurately control the weights (Mw) and of the two copolymers were Mw = 16.9

Scheme 1. Synthetic Routes of the Macromonomer and Brush Copolymer

30857 https://dx.doi.org/10.1021/acsami.0c08170 ACS Appl. Mater. Interfaces 2020, 12, 30856−30861 ACS Applied Materials & Interfaces www.acsami.org Research Article

Table 1. Polymerization Results and Thermal Properties of 2.2. Optical Properties. The photophysical properties of Copolymers the two polymers (MM and BP) were investigated using ultraviolet−visible (UV−vis) spectroscopy. The key physical · −1 a Đ ° b copolymers yields (%) Mn Mw (kg mol ) Td ( C) properties are summarized in Table 2. Both of our polymers MM 87 13.5 16.9 1.25 352 showed a very similar absorption spectrum from 300 to 500 BP 83 39.5 102.0 2.58 386 nm in the visible region (Figure 2). This is very similar to that aDetermined by GPC in THF based on polystyrene standards. bDecomposition temperature, determined by TGA in nitrogen, based on 5% weight loss.

Đ kg/mol with a = 1.25 for MM and Mw = 102.0 kg/mol with a Đ =2.58forBP, as determined by gel permeation chromatography (GPC) using polystyrenes standard and CHCl3 as the eluent. The thermal properties of the copolymers were determined by thermogravimetric analysis (TGA) under a nitrogen atmosphere at a heating rate of 10 °C/min. The two Figure 2. UV−vis absorption spectra of the copolymers in the film polymers (MM and BP) showed good thermal stability with states. onset decomposition temperatures (Td) corresponding to a 5% ° weight loss at 352 and 386 C, respectively, as shown in Table of regioregular P3HT.16 The two polymers showed the same 1. absorption maxima at 448 nm. Since the content of the The synthesis of the macromonomer via KCTP is the crucial backbone is relatively low compared to the P3HT side chains, step in our synthesis. Normally, this polymerization is backbone absorption might be overlapped with that of P3HT quenched with HCl; however, since the macromonomer has leading to almost identical spectra. Absorption maxima for thin trimethyltin groups attached that are sensitive to acidic films were shifted from 448 to 518 nm for both the polymers. conditions, the reaction was just quenched with MeOH. The 70 nm red shift indicated a very strong aggregation in NMR spectrum (Figure S6)ofMM showed a clear signal at solid state, which is reasonable because the major component 0.43 ppm, which is consistent with the trimethyltin signal of of the polymers is a regioregular17 P3HT chain. the initiator compound 4 at 0.41 ppm (Figure S4). The 2.3. Electrochemical Properties. Electrochemical spectra integration ratio of the methyl groups with the aromatic of the two polymers MM and BP were investigated by cyclic protons on the thiophenes indicated that the DP of the P3HT voltammetry (CV). The CV curves and their corresponding chains is around 20, which is in good agreement with the data (Figure 3 and Table 2) indicate that these polymers are starting material ratio of the thiophene Grignard reagents and the initiator of 38. Theoretically, each side of the BDT unit should attach 19 thiophenes, plus one from the initiator itself totaling 20. ICP-MS was employed to investigate the tin content that was found to be 2.13% by weight. With this result, we were able to control the amount of the monomer compound 6 to keep a 1:1 ratio, which is a crucial issue that previous studies were unable to solve. Then, graft polymer BP was obtained that showed a relatively high DP of around 3, which is higher than the published work with grafting through method.4 There were some higher-molecular-weight polymers left after Soxlet purification, which were extracted out by chlorobenzene. Our result indicates that this method can Figure 3. Cyclic voltammograms of polymers in CH3CN/0.1 M synthesize graft polymers with a higher DP if there are no Bu NPF at 50 mV/s. solubility issues. The average molecular weights of the two 4 6 polymers were compared, and it showed a significant increase in Mw from 16.9 to 102 kg/mol. Further evidence from elemental analysis and NMR (Figure S7) confirmed that the electroactive. The redox potentials were first referenced to the components of the monomer 6 were indeed found in the ferrocene/ferrocenium redox couple (Fc/Fc+), which is at 0.47 polymer BP. Elemental analysis was in good agreement with V vs a saturated calomel electrode (SCE). The redox potential the theoretical data: it was found that the N content of BP is of Fc/Fc+ was then assumed to be at −4.8 eV relative to 0.57% as it is supposed to be, while it is 0% for MM. vacuum.18

Table 2. Optical and Electrochemical Properties of the Two Copolymers λ a fi λ fi λ solution s,max (nm) lm f,max (nm) lm edge (nm) opt b ec copolymers Abs. Abs. Abs. Eg (eV) HOMO (eV) LUMO (eV) Eg (eV) MM 448 518 644 1.93 −4.95 −2.60 2.35 BP 448 518 649 1.91 −5.05 −2.66 2.39 aMeasured in a chloroform solution. bBand gap estimated from the optical absorption band edge of the films.

30858 https://dx.doi.org/10.1021/acsami.0c08170 ACS Appl. Mater. Interfaces 2020, 12, 30856−30861 ACS Applied Materials & Interfaces www.acsami.org Research Article

Then, the highest occupied molecular orbital (HOMO)/ of 2.39 ± 0.57 (104) °/T·m(Table 3). Since these polymers lowest unoccupied molecular orbital (LUMO) energy levels contain P3HT brushes, it is appropriate to make similar ec and electrochemical energy gaps (Eg ) of our copolymers were calculated as per the following equations Table 3. Measured Verdet Constant and Faraday Rotation of BP and Related Materials HOMO=− (Eox + 4.33) (eV) verdet constant rotation at 4° · μ μ LUMO=− (Ered + 4.33) (eV) (10 /T m) thickness ( m) 148G ( deg) ± ± a ± ec substrate 0.0292 0.00025 1000 3 841 20 EEE=−( ) (eV) b g ox red BP 2.4 ± 0.6 0.0818 ± 0.0028 32 ± 9 ± ± c ± The onset oxidation potentials (E ) were found to be 0.62 and polystyrene 0.0167 0.0010 10.0 0.2 21 3 ox ± ± c ± 0.72 V for MM and BP, corresponding to the HOMO energy RRP3HT 4.3 1.5 0.108 0.017 67 23 levels of −4.95 and −5.05 eV, respectively. The LUMO energy aMeasured by precision micron calipers. bDetermined by AFM. c levels of MM and BP were calculated to be −2.60 and −2.66 Determined by profilimeter. eV, indicating a low band gap of 2.35 and 2.39 eV, respectively. fi The optical band gaps were calculated from their lm measurements on RRP3HT for comparison and to reveal absorption, and they were found to be 1.93 eV for MM and additional details on the morphology. Gangopadhyay and ff 1.91 eV for BP.Itdidnotshowlargedierences in Persoons reported a Verdet Constant for RRP3HT of 6.25 ± electrochemical properties, which is reasonable because the 0.3 (104) °/T·m, employing a similar instrumental method.12 P3HT side chains of the polymers contributed much more In our laboratory, we obtained a Verdet Constant of 4.32 ± 1.5 fi than the backbones. Therefore, the nal properties were found (104) °/T·m for RRP3HT in good agreement with this to be the same as the properties of P3HT side chains. literature report. These data suggest that BP forms a structure 2.4. Morphology Investigation. To investigate the similar to that of RRP3HT. Indeed, thermally annealed thin morphology and packing of this graft polymer BP, grazing films of RRP3HT do not exhibit a Faraday effect or magneto- incidence wide-angle X-ray scattering two-dimensional (GI- optical activity. The preservation of the magneto-optical effect fi WAXS-2D) was measured for the polymer lms (Figure 4). in BP suggests that the RRP3HT side chains form extended, disordered domains, which is corroborated by the 2D GIWAXS measurements. Moreover, theory predicts that such domains should yield a Faraday response.20 It is interesting to note that the inclusion of an acceptor moiety within the polymer backbone does not appear to yield a large perturbation on the magneto-optic activity of P3HT. Within the context of this sample, we thus infer that it is the RRP3HT brush units that are solely responsible for the rotation of plane- polarized light in these studies. The precise origin of the Faraday effect in these materials is still an open question; Figure 4. Two-dimensional GIWAXS scattering patterns of BP films however, since it is a diamagnetic material of low symmetry, (left) and one-dimensional (1D)-linecuts in out-of-plane (q ) the magneto-optic activity must arise through Faraday B- z 21 fi direction and in-plane (qxy) direction (right). terms. This particular Faraday term quanti es optical activity attributed to a magnetic field-induced mixing of nondegenerate The polymer films were coated onto the polished side of a electronic states. This theoretical basis combined with the silicon wafer. The polymer shows a broad arc scattering profile, strong dependence on regioregularity and sample processing corresponding to π−π stacking, which indicates the amorphous implicates the mixing of electronic states localized on close- nature of the polymer. Unlike, P3HT, which has an edge-on packed RRP3HT chains. orientation and exhibits sharp out-of-plane (100), (200), and (300) scattering peaks, this polymer exhibits no such peaks. In 3. CONCLUSIONS fi out-of-plane qz direction, the polymer exhibits broad peaks at In conclusion, we have demonstrated a nely designed grafting 0.3 and 0.5 Å−1, corresponding to the distances 20.9 and 12.5 through approach for synthesizing fully conjugated graft Å−1, respectively./ polymers. A tin contained initiator was used for the synthesis 2.5. Faraday Effect. To corroborate the results obtained of macromonomers (MM) by employing Kumada catalyst from UV−visible spectroscopy and GIWAXS measurements, transfer polycondensation. The content of the trimethyltin we employed magneto-optical polarimetry on these samples, as functional group was precisely determined, which lead to good this technique is highly sensitive to morphology and stacking control of the 1:1 monomer ratio for the later copolymeriza- of P3HT materials.15 Magneto-optical activity was measured tion to obtain a graft polymer (BP). The structures of the using a Faraday polarimeter under a low-frequency AC newly developed polymers were characterized and analyzed, magnetic field through simultaneous balanced detection and and experimental results were in good agreement with homodyne detection (Figure S1).19 A full description of our theoretical ones. The optical and electrochemical properties instrument is found in the Supporting Information. Measure- were studied, which were found to be the same as those of the ments were performed using a 532 nm coherent light source P3HT side chains. The Faraday effect of BP was investigated, and measured in triplicate at five different field strengths across and it was found to be in accord with that exhibited by three separate thin-film samples of BP. High-quality thin films RRP3HT. Based on this result, we infer that the acceptor of BP (formed from spin coating; 81.8 ± 2.8 nm, measured by backbone permits the P3HT brush units to form a similar atomic force microscopy (AFM)) exhibited a Verdet constant mesoscale structure to that displayed by RRP3HT. As more

30859 https://dx.doi.org/10.1021/acsami.0c08170 ACS Appl. Mater. Interfaces 2020, 12, 30856−30861 ACS Applied Materials & Interfaces www.acsami.org Research Article “graft-through” type polymers are produced through selective ■ AUTHOR INFORMATION chemical functionalization, Faraday activity can serve as a Corresponding Authors reporter on the morphological characteristics of the RRP3HT Jeffrey J. Rack − Department of Chemistry and Chemical side chains and their electronic coupling to the acceptor Biology, Laboratory for Magneto-Optic Spectroscopy, University moieties in the polymer backbone. This work thus provides a of New Mexico, Albuquerque, New Mexico 87131, United simple and effective method for synthesizing fully conjugated States; orcid.org/0000-0001-6121-879X; Email: jrack@ graft polymers and to explore new properties and applications unm.edu of these systems. Luping Yu − Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, 4. EXPERIMENTAL SECTION United States; Email: [email protected] 1H NMR and 13C NMR spectra were recorded on a Bruker DRX-500 Authors spectrometer. Matrix-assisted laser desorption ionization time-of-flight Xunshan Liu − Department of Chemistry and The James Franck (MALDI-TOF) mass spectra were recorded using a Bruker Institute, The University of Chicago, Chicago, Illinois 60637, Ultraflextreme MALDI-TOF mass spectrometer with dithranol as − − United States; orcid.org/0000-0003-1537-258X the ionization matrix. Gas chromatography mass spectra (GC MS) Emigdio E. Turner − Department of Chemistry and Chemical were measured with Agilent SQ GC−MS (5977A single quad MS and 7890B GC). Ultraviolet−visible−near infrared (UV−vis−NIR) Biology, Laboratory for Magneto-Optic Spectroscopy, University spectra of the polymers were measured on a SHIMADZU UV-3600 of New Mexico, Albuquerque, New Mexico 87131, United spectrometer. The elemental analyses of the polymers were performed States on an Elementar Vario EL III element analyzer for C, H, Br, and S Valerii Sharapov − Department of Chemistry and The James determination. Thermogravimetric analyses (TGA) were performed Franck Institute, The University of Chicago, Chicago, Illinois under nitrogen at a heating rate of 10 °C min−1 using a SHIMADZU 60637, United States; orcid.org/0000-0002-2828-0468 TGA-50 analyzer. The average molecular weight and polydispersity Dafei Yuan − Department of Chemistry and The James Franck index (Đ) of the polymers were determined using Waters 1515 gel Institute, The University of Chicago, Chicago, Illinois 60637, permeation chromatography (GPC) analysis with CHCl3 as eluent United States; orcid.org/0000-0001-5914-2060 and polystyrene as standard; there are two detectors for the Mohammad A. Awais − − Department of Chemistry and The instrument, refractive index detector and UV vis detector; in this James Franck Institute, The University of Chicago, Chicago, study, all of the molecular weights were collected from the traces with Illinois 60637, United States the UV−vis detector. Electrochemical redox potentials were obtained by cyclic voltammetry (CV) using a three-electrode configuration and Complete contact information is available at: an electrochemistry workstation (AUTOLAB PGSTAT12). CV was https://pubs.acs.org/10.1021/acsami.0c08170 conducted on an electrochemistry workstation with the polymer thin film on a Pt working electrode, Pt as the counter electrode as well, and Notes Ag/AgCl as a reference electrode in a 0.1 M tetra-n-butylammonium The authors declare no competing financial interest. hexafluorophosphate acetonitrile solution at a scan rate of 50 mV s−1. ICP-MS data was obtained with an Agilent 7700x ICP-MS and ■ ACKNOWLEDGMENTS analyzed using ICP-MS MassHunter version B01.03. A commercially available standard E2-TB01060 from the company Inorganic Ventures This work was supported by NSF (Chem-1802274), partially was used. Ten milligrams of vacuum-dried sample was weighed in a supported by the University of Chicago Materials Research glass vial. One milliliter of metal-free 70% nitric acid was added to Science and Engineering Center, which is funded by the each vial and then incubated on 80 °C water bath for 3 h until all solid National Science Foundation under award number DMR- samples dissolved. The digested sample in 70% nitric acid was diluted 1420709. This research used resources of the Advanced 35 times by DI water to prepare a 2% nitric acid solution; then, Photon Source, a U.S. Department of Energy (DOE) Office of further diluted by 2% nitric acid until the ICP-MS read out below 500 Science User Facility operated for the DOE Office of Science ppb. Faraday rotation was detected using a homodyne detection by Argonne National Laboratory under Contract No. DE- scheme. A 532 nm diode laser was initially polarized at 45°. This light AC02-06CH11357. We thank Wenbo Han for the ICP-MS fi was directed through a thin- lm sample mounted in the center of a measurements. J.J.R. acknowledges NSF (CHE-1856492) for solenoid. The reference frequency generated by a Stanford research fi fi support of this work. E.E.T. acknowledges the NSF for a instruments SR830 lock-in ampli er was further ampli ed and used to Graduate Research Fellowship Program for support (DGE- generate a low-frequency magnetic field. The polarizing beam splitter positioned after the sample converts changes in polarization into 1418062). intensity changes in two beams, which are then detected by a ■ REFERENCES Newport nirvana 2007 balanced detection system (Figure S1). Multiple measurements are made while incrementally increasing the (1) Wu, W.; Liu, Y.; Zhu, D. π-Conjugated Molecules with Fused magnetic field generated by the solenoid, and a Verdet constant is Rings for Organic Field-effect Transistors: Design, Synthesis and extracted by fitting polarization measurements against magnetic field Applications. Chem. Soc. Rev. 2010, 39, 1489−1502. measurements using a least-squares linear regression. (2) Wang, C.; Dong, H.; Jiang, L.; Hu, W. Organic Semiconductor Crystals. Chem. Soc. Rev. 2018, 47, 422−500. (3) Lu, L.; Zheng, T.; Wu, Q.; Schneider, A. M.; Zhao, D.; Yu, L. ■ ASSOCIATED CONTENT Recent Advances in Bulk Heterojunction Polymer Solar Cells. Chem. − *sı Supporting Information Rev. 2015, 115, 12666 12731. (4) Zeigler, D. F.; Mazzio, K. A.; Luscombe, C. K. Fully Conjugated The Supporting Information is available free of charge at Graft Copolymers Comprising a P-Type Donor−Acceptor Backbone https://pubs.acs.org/doi/10.1021/acsami.0c08170. and Poly(3-hexylthiophene) Side Chains Synthesized Via a “Graft ” − It includes a detailed synthesis of the monomers and Through Approach. Macromolecules 2014, 47, 5019 5028. (5) Wang, J.; Lu, C.; Mizobe, T.; Ueda, M.; Chen, W.-C.; polymers; characterization methods (PDF) Higashihara, T. Synthesis and Characterization of All-Conjugated

30860 https://dx.doi.org/10.1021/acsami.0c08170 ACS Appl. Mater. Interfaces 2020, 12, 30856−30861 ACS Applied Materials & Interfaces www.acsami.org Research Article

Graft Copolymers Comprised of n-Type or p-Type Backbones and Poly(3-hexylthiophene) Side Chains. Macromolecules 2013, 46, 1783− 1793. (6) Riera-Galindo, S.; Leonardi, F.; Pfattner, R.; Mas-Torrent, M. Organic Semiconductor/Polymer Blend Films for Organic Field- Effect Transistors. Adv. Mater. Technol. 2019, 4, No. 1900104. (7) Wang, G.; Swick, S. M.; Matta, M.; Mukherjee, S.; Strzalka, J. W.; Logsdon, J. L.; Fabiano, S.; Huang, W.; Aldrich, T. J.; Yang, T.; Timalsina, A.; Powers-Riggs, N.; Alzola, J. M.; Young, R. M.; DeLongchamp, D. M.; Wasielewski, M. R.; Kohlstedt, K. L.; Schatz, G. C.; Melkonyan, F. S.; Facchetti, A.; Marks, T. J. Photovoltaic Blend Microstructure for High Efficiency Post-Fullerene Solar Cells. To Tilt or Not To Tilt? J. Am. Chem. Soc. 2019, 141, 13410−13420. (8) Hwang, Y.-J.; Earmme, T.; Courtright, B. A. E.; Eberle, F. N.; Jenekhe, S. A. n-Type Semiconducting Naphthalene Diimide-Perylene Diimide Copolymers: Controlling Crystallinity, Blend Morphology, and Compatibility toward High-performance All-Polymer Solar Cells. J. Am. Chem. Soc. 2015, 137, 4424−4434. (9) Chatterjee, S.; Karam, T. E.; Rosu, C.; Wang, C.-H.; Youm, S. G.; Li, X.; Do, C.; Losovyj, Y.; Russo, P. S.; Haber, L. H.; Nesterov, E. E. Silica−Conjugated Polymer Hybrid Fluorescent Nanoparticles: Preparation by Surface-Initiated Polymerization and Spectroscopic Studies. J. Phys. Chem. C 2018, 122, 6963−6975. (10) Khanduyeva, N.; Senkovskyy, V.; Beryozkina, T.; Bocharova, V.; Simon, F.; Nitschke, M.; Stamm, M.; Gro tzschel, R.; Kiriy, A. Grafting of Poly(3-hexylthiophene) from Poly(4-bromostyrene) Films by Kumada Catalyst-Transfer Polycondensation: Revealing of the Composite Films Structure. Macromolecules 2008, 41, 7383−7389. (11) Lutz, J. P.; Hannigan, M. D.; McNeil, A. J. Polymers Synthesized via Catalyst-transfer Polymerization and Their Applica- tions. Coord. Chem. Rev. 2018, 376, 225−247. (12) Gangopadhyay, P.; Voorakaranam, R.; Lopez-Santiago, A.; Foerier, S.; Thomas, J.; Norwood, R. A.; Persoons, A.; Peyghambarian, N. Faraday Rotation Measurements on Thin Films of Regioregular Alkyl-Substituted Polythiophene Derivatives. J Phys. Chem. C 2008, 112, 8032−8037. (13) Araoka, F.; Abe, M.; Yamamoto, T.; Takezoe, H. Large Faraday Rotation in a π-Conjugated Poly(arylene ethynylene) Thin Film. Appl. Phys. Express 2009, 2, No. 011501. (14) Koeckelberghs, G.; Vangheluwe, M.; Doorsselaere, K. V.; Robijns, E.; Persoons, A.; Verbiest, T. Regioregularity in Poly(3- alkoxythiophene)s: Effects on the Faraday Rotation and Polymer- ization Mechanism. Macromol. Rapid Commun. 2006, 27, 1920−1925. (15) Gangopadhyay, P.; Koeckelberghs, G.; Persoons, A. Magneto- optic Properties of Regioregular Polyalkylthiophenes. Chem. Mater. 2011, 23, 516−521. (16) Fei, Z.; Boufflet, P.; Wood, S.; Wade, J.; Moriarty, J.; Gann, E.; Ratcliff, E. L.; McNeill, C. R.; Sirringhaus, H.; Kim, J.-S.; Heeney, M. Influence of Backbone Fluorination in Regioregular Poly(3-alkyl-4- fluoro)thiophenes. J. Am. Chem. Soc. 2015, 137, 6866−6879. (17) Yuan, M.; Okamoto, K.; Bronstein, H. A.; Luscombe, C. K. Constructing Regioregular Star Poly(3-hexylthiophene) via Externally Initiated Kumada Catalyst-Transfer Polycondensation. ACS Macro Lett. 2012, 1, 392−395. (18) Wang, M.; Hu, X.; Liu, P.; Li, W.; Gong, X.; Huang, F.; Cao, Y. Donor-acceptor Conjugated Polymer Based on Naphtho[1,2-c:5,6- c]bis[1,2,5]thiadiazole for High-performance Polymer Solar cells. J. Am. Chem. Soc. 2011, 133, 9638−9641. (19) Chang, C.-Y.; Wang, L.; Shy, J.-T.; Lin, C.-E.; Chou, C. Sensitive Faraday Rotation Measurement with Auto-balanced Photo- detection. Rev. Sci. Instrum. 2011, 82, No. 063112. (20) Louant, O.; Liegeois,́ V.; Verbiest, T.; Persoons, A.; Champagne, B. Faraday Effect in Stacks of Aromatic Molecules. J. Phys. Chem. C 2017, 121, 15348−15352. (21) Barron, L. D. Molecular Light Scattering and Optical Activity, 2nd ed.; Cambridge University Press: Cambridge, 2004.

30861 https://dx.doi.org/10.1021/acsami.0c08170 ACS Appl. Mater. Interfaces 2020, 12, 30856−30861